Sustained Mnemonic Response in the Human Middle Frontal Gyrus during On-Line Storage of Spatial Memoranda

Leung, Hoi‐Chung; Gore, John C.; Goldman‐Rakic, Patricia S.

doi:10.1162/08989290260045882

Cited by 290 publications

(223 citation statements)

References 43 publications

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“…However, another study found that DLPFC activity was present during maintenance even when no decision or response was required (Wagner et al, 2001). DLPFC may also be preferentially engaged in maintenance of spatial materials (Leung et al, 2002). In summary, DLPFC activity is sometimes shown to be temporally associated with delays that emphasize maintenance, but has a greater response with high WM loads and when manipulation and response preparation are required.…”

Section: Discussionmentioning

confidence: 98%

“…While some studies do not find DLPFC activity during a delay periods that emphasize maintenance (Rowe and Passingham, 2001;Rowe et al, 2000), many others do (Chein and Fiez, 2001;Courtney et al, 1997;Leung et al, 2002;Rypma and D'Esposito, 1999). Task attributes that may determine whether DLPFC is engaged during the delay period of tasks that emphasize maintenance include the level WM load, whether response preparation is required, and the type of material being maintained.…”

Section: Discussionmentioning

confidence: 99%

“…One involves extending the length of the delay epoch so that the residual HDR to encode decays (Chein and Fiez, 2001;Cohen et al, 1997;Jha and McCarthy, 2000;Leung et al, 2002;Rypma and D'Esposito, 1999). This strategy isolates activity specific to delay processes.…”

Section: Introductionmentioning

confidence: 99%

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Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI

et al. 2003

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This study describes the neural circuitry underlying temporally separated components of working memory (WM) performance-stimulus encoding, maintenance of information during a delay, and the response to a probe. While other studies have applied event-related fMRI to separate epochs of WM tasks, this study differs in that it employs a methodology that does not make any a priori assumptions about the shape of the hemodynamic response (HDR). This is important because no one model of the HDR is valid across the range of activated brain regions and stimulus types. Systematic modeling inaccuracies may lead to the misattribution of activity to adjacent events. Twelve healthy subjects performed a numerical version of the Sternberg Item Recognition Paradigm adapted for rapid presentation event-related fMRI. This paradigm emphasized maintenance rather than manipulative WM processes and used a subcapacity WM load. WM trials with different delay lengths were compared to fixation. The HDR of the entire WM trial for each trial type was estimated using a finite impulse response (FIR). Regional activity associated with the Encode, Delay, and Probe epochs was identified using contrasts that were based on the FIR estimates and by examining the HDRs. Each epoch was associated with a distinct but overlapping pattern of regional activity. Activation of the dorsolateral prefrontal cortex, thalamus, and basal ganglia was exclusively associated with the probe. This suggests that frontostriatal neural circuitry participates in selecting an appropriate response based on the contents of WM.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

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Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI

et al. 2003

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“…These findings, thus, are contrary to the view that the DLPFC simply maintains task relevant representations. However, Leung, Gore and GoldmanRakic [36] recently demonstrated that the DLPFC does not sustain a significant level of activity throughout a 18 s delay when maintaining three faces in memory, but does so if five faces are required to be remembered. Two recent studies from our laboratory have also detected significant effects of memory load on delay period DLPFC activity during a face [42] and letter [43] working memory task.…”

Section: Number Of Itemsmentioning

confidence: 99%

Persistent activity in the prefrontal cortex during working memory

Curtis

D’Esposito

2003

Trends in Cognitive Sciences

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The dorsolateral prefrontal cortex (DLPFC) plays a crucial role in working memory. Notably, persistent activity in the DLPFC is often observed during the retention interval of delayed response tasks. The code carried by the persistent activity remains unclear, however. We critically evaluate how well recent findings from functional magnetic resonance imaging studies are compatible with current models of the role of the DLFPC in working memory. These new findings suggest that the DLPFC aids in the maintenance of information by directing attention to internal representations of sensory stimuli and motor plans that are stored in more posterior regions.Working memory refers to the temporary representation of information that was just experienced or just retrieved from long-term memory. These active representations are short-lived, but can be maintained for longer periods of time through active rehearsal strategies, and can be subjected to various operations that manipulate the information in such a way that makes it useful for goaldirected behavior. Most definitions of working memory include both storage and (executive) control components [1]. Cognitive neuroscientists are searching for ways to disassociate the separate components of working memory in attempts to localize and clearly characterize their neural implementation. The prefrontal cortex (PFC) is thought to be the most important substrate for working memory (Fig. 1). Two key findings from studies of monkeys performing delayed response tasks suggest a crucial role for the PFC in working memory. First, experimental lesions of the principal sulcus in the dorsolateral prefrontal cortex (DLPFC) cause delay-dependent impairments [2][3][4]. That is, forgetting increases not only when a delay is imposed but increases with the length of the delay. Second, neurophysiological unit recordings from the DLPFC often show persistent, sustained levels of neuronal firing during the retention interval of delayed response Fig. 1. Lateral surface of (a) macaque and (b) human brain. The PFC is composed of lateral, medial, and orbital sectors that are believed to be functionally distinct given the selective effects of damage and distribution of afferent and efferent projections. The tinted areas correspond to those defined by Petrides and Pandya [71] based on cytoarchitecture and connectivity. Notably, the mid-DLPFC comprises areas 46 and 9/46 and the mid-VLPFC comprises areas 45 and 47/12. Note that much of area 46 lies in the depths of the principle sulcus of the monkey and the intermediate frontal sulcus of the human. Frontal premotor regions are also highlighted. The frontal eye field (F) in the macaque lies in the anterior bank of the arcuate sulcus in area 8A. In the human, F is found in the vicinity of the precentral sulcus and superior frontal sulcus junction (area 6 and maybe the caudal-most portion of 8A). The frontal eye field is a premotor region involved in the control of eye movements. Broca's area (B, area 44) is also a premotor area that is involved in the product...

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“…Comparison of these data with those on regional differences in pyramidal cell structure (Lund et al, 1993;Elston et al, 1999bElston et al, , 2005aElston, 2000;Elston and Rockland, 2002) reveals some interesting functional parallels. For example, highly branched, spinous neurons in gPFC are characterized by their tonic activity, which is sustained despite intervention from distractors; less branched and less spinous neurons in sensory association cortex are characterized by tonic activity, which desists following presentation of distractors; and the least branched and least spinous cells in V1, for example, are characterized by phasic discharge properties (Fuster and Alexander, 1971;Ashford and Fuster, 1985;Koch and Fuster, 1989;Constantinidis and Steinmetz, 1996;Miller et al, 1996;Leung et al, 2002;Sakai et al, 2002). Accepting the parallel between neuron structure and function, the present results suggest that species differences in prefrontal functions such as conceptual thinking, prioritizing, and planning may be attributed in part at least to specializations in cortical microcircuitry.…”

Section: Structure/function Relationshipmentioning

confidence: 99%

Specializations of the granular prefrontal cortex of primates: Implications for cognitive processing

et al. 2005

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The biological underpinnings of human intelligence remain enigmatic. There remains the greatest confusion and controversy regarding mechanisms that enable humans to conceptualize, plan, and prioritize, and why they are set apart from other animals in their cognitive abilities. Here we demonstrate that the basic neuronal building block of the cerebral cortex, the pyramidal cell, is characterized by marked differences in structure among primate species. Moreover, comparison of the complexity of neuron structure with the size of the cortical area/region in which the cells are located revealed that trends in the granular prefrontal cortex (gPFC) were dramatically different to those in visual cortex. More specifically, pyramidal cells in the gPFC of humans had a disproportionately high number of spines. As neuron structure determines both its biophysical properties and connectivity, differences in the complexity in dendritic structure observed here endow neurons with different computational abilities. Furthermore, cortical circuits composed of neurons with distinguishable morphologies will likely be characterized by different functional capabilities. We propose that 1. circuitry in V1, V2, and gPFC within any given species differs in its functional capabilities and 2. there are dramatic differences in the functional capabilities of gPFC circuitry in different species, which are central to the different cognitive styles of primates. In particular, the highly branched, spinous neurons in the human gPFC may be a key component of human intelligence.

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Sustained Mnemonic Response in the Human Middle Frontal Gyrus during On-Line Storage of Spatial Memoranda

Cited by 290 publications

References 43 publications

Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI

Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI

Persistent activity in the prefrontal cortex during working memory

Specializations of the granular prefrontal cortex of primates: Implications for cognitive processing

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